[core] Offline download must clear batch buffer at load interrupt

Otherwise, the stale buffer data are processed again at the
repeated load. It is causing various problems like missing load
completion notification or crashes (if the previously used observer
instance has been deleted).

2 files changed, 83 insertions, 1 deletions

diff --git a/platform/default/src/mbgl/storage/offline_download.cpp b/platform/default/src/mbgl/storage/offline_download.cpp
index d5cf7e4fe1..98eb1d3884 100644
--- a/platform/default/src/mbgl/storage/offline_download.cpp
+++ b/platform/default/src/mbgl/storage/offline_download.cpp
@@ -379,6 +379,7 @@ void OfflineDownload::deactivateDownload() {
     requiredSourceURLs.clear();
     resourcesRemaining.clear();
     requests.clear();
+    buffer.clear();
 }
 
 void OfflineDownload::queueResource(Resource&& resource) {
diff --git a/test/storage/offline_download.test.cpp b/test/storage/offline_download.test.cpp
index ebe3f82ee9..c1a9bb73f4 100644
--- a/test/storage/offline_download.test.cpp
+++ b/test/storage/offline_download.test.cpp
@@ -757,7 +757,6 @@ TEST(OfflineDownload, Deactivate) {
     test.loop.run();
 }
 
-
 TEST(OfflineDownload, AllOfflineRequestsHaveLowPriorityAndOfflineUsage) {
     OfflineTest test;
     auto region = test.createRegion();
@@ -947,3 +946,85 @@ TEST(OfflineDownload, ResourceOfflineUsageUnset) {
     test.loop.run();
 }
 #endif // __QT__
+
+// Test verifies that resource batch buffer is cleared at loading interrupt.
+TEST(OfflineDownload, InterruptAndResume) {
+    OfflineTest test;
+    auto region = test.createRegion();
+    ASSERT_TRUE(region);
+    OfflineDownload download(region->getID(),
+                             OfflineTilePyramidRegionDefinition(
+                                 "http://127.0.0.1:3000/style.json", LatLngBounds::world(), 0.0, 0.0, 1.0, true),
+                             test.db,
+                             test.fileSource);
+
+    test.fileSource.styleResponse = [&](const Resource& resource) {
+        EXPECT_EQ("http://127.0.0.1:3000/style.json", resource.url);
+        return test.response("style.json");
+    };
+
+    test.fileSource.spriteImageResponse = [&](const Resource& resource) {
+        EXPECT_TRUE(resource.url == "http://127.0.0.1:3000/sprite.png" ||
+                    resource.url == "http://127.0.0.1:3000/sprite@2x.png");
+        return test.response("sprite.png");
+    };
+
+    test.fileSource.imageResponse = [&](const Resource& resource) {
+        EXPECT_EQ("http://127.0.0.1:3000/radar.gif", resource.url);
+        return test.response("radar.gif");
+    };
+
+    test.fileSource.spriteJSONResponse = [&](const Resource& resource) {
+        EXPECT_TRUE(resource.url == "http://127.0.0.1:3000/sprite.json" ||
+                    resource.url == "http://127.0.0.1:3000/sprite@2x.json");
+        return test.response("sprite.json");
+    };
+
+    test.fileSource.glyphsResponse = [&](const Resource&) { return test.response("glyph.pbf"); };
+
+    test.fileSource.sourceResponse = [&](const Resource& resource) {
+        EXPECT_EQ("http://127.0.0.1:3000/streets.json", resource.url);
+        return test.response("streets.json");
+    };
+
+    test.fileSource.tileResponse = [&](const Resource& resource) {
+        const Resource::TileData& tile = *resource.tileData;
+        EXPECT_EQ("http://127.0.0.1:3000/{z}-{x}-{y}.vector.pbf", tile.urlTemplate);
+        EXPECT_EQ(1, tile.pixelRatio);
+        EXPECT_EQ(0, tile.x);
+        EXPECT_EQ(0, tile.y);
+        EXPECT_EQ(0, tile.z);
+        return test.response("0-0-0.vector.pbf");
+    };
+
+    auto observer = std::make_unique<MockObserver>();
+    bool interrupted = false;
+    observer->statusChangedFn = [&](OfflineRegionStatus status) {
+        if (!interrupted && status.completedResourceCount > 0) {
+            interrupted = true;
+            assert(!status.complete());
+            test.loop.schedule([&]() {
+                download.setState(OfflineRegionDownloadState::Inactive);
+                test.loop.stop();
+            });
+        }
+    };
+
+    download.setObserver(std::move(observer));
+    download.setState(OfflineRegionDownloadState::Active);
+    test.loop.run();
+
+    auto newObserver = std::make_unique<MockObserver>();
+    newObserver->statusChangedFn = [&](OfflineRegionStatus status) {
+        if (status.complete()) {
+            EXPECT_EQ(status.completedTileCount, status.requiredTileCount);
+            EXPECT_EQ(264u, status.completedResourceCount); // 256 glyphs, 2 sprite images, 2 sprite jsons, 1 tile, 1
+                                                            // style, source, image
+            test.loop.stop();
+        }
+    };
+
+    download.setObserver(std::move(newObserver));
+    download.setState(OfflineRegionDownloadState::Active);
+    test.loop.run();
+}